| Abstract: | Previous experiments in this laboratory demonstrated a progressive decrease in cell-mediated cytotoxicity (CMC) against allogeneic tumor cells by immune spleen cells from mice repeatedly immunized with those tumor cells. In the present study, immune spleen cells, obtained at specified intervals during the course of multiple immunizations of BALB/c mice with EL-4 lymphoma cells, were tested for CMC against EL-4 target cells pretreated with anti-EL-4 serum which had been obtained from singly or repeatedly immunized animals. Cytolysis of EL-4 cells was measured by a 51Cr-release assay. The results indicate that blocking of CMC in an allogeneic tumor model may occur by two pathways. First, antigen or antigen-antibody complexes present in the immunized animal may bind in vivo to the antigen receptor sites of of sensitized effector cells that are used in the in vitro CMC assay, thereby blocking their interaction with tumor cells. Second, immune serum that is added to the in vitro CMC assay may contain highly avid antibodies, as well as antigen-antibody complexes, that bind to tumor cells and thereby block interaction with sensitized effector cells. The identification of these elements may be of prognostic significance in certain clinical situations. |
